1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system and to a head gimbal assembly, a head arm assembly, and a magnetic disk drive each of which incorporates the magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
It is known that there are types of magnetic heads for the perpendicular magnetic recording system one of which is a single-pole head as disclosed in Japanese Published Patent Application 2003-296906 and another one of which is a shield-type head as disclosed in U.S. Pat. No. 4,656,546 and Japanese Published Patent Application 2004-295987.
The single-pole head comprises: a medium facing surface that faces toward a recording medium; a coil for generating a magnetic field corresponding to data to be written on the recording medium; a pole layer (main pole) having an end face located in the medium facing surface, allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough, and generating a write magnetic field for writing the data on the recording medium by means of the perpendicular magnetic recording system; an auxiliary pole having an end face located in the medium facing surface and having a portion that is located away from the medium facing surface and coupled to the pole layer; and a gap layer made of a nonmagnetic material and provided between the pole layer and the auxiliary pole. In the medium facing surface, the end face of the auxiliary pole is located backward of the end face of the pole layer along the direction of travel of the recording medium.
The shield-type head comprises: a medium facing surface that faces toward a recording medium; a coil for generating a magnetic field corresponding to data to be written on the recording medium; a pole layer having an end face located in the medium facing surface, allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough, and generating a write magnetic field for writing the data on the recording medium by means of the perpendicular magnetic recording system; a shield layer having an end face located in the medium facing surface and having a portion that is located away from the medium facing surface and coupled to the pole layer; and a gap layer made of a nonmagnetic material and provided between the pole layer and the shield layer. In the medium facing surface, the end face of the shield layer is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific small space. In the shield-type head, the shield layer is capable of making the magnetic field gradient abrupt by taking in the magnetic flux generated from the pole layer. As a result, the shield-type head is capable of further improving the linear recording density. The magnetic field gradient means an amount of change of components orthogonal to the surface of the recording medium among components of the magnetic field generated from the pole layer, the amount of change being taken per unit length along the direction of travel of the recording medium.
In each of the single-pole head and the shield-type head, the pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in the medium facing surface, and defines the track width. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width. For example, the wide portion is equal in width to the track width defining portion at the interface with the track width defining portion, and gradually increases in width as the distance from the medium facing surface increases and then maintains a specific width to the end of the wide portion.
It is a reduction in track width, that is, a reduction in width of the end face of the pole layer located in the medium facing surface, and improvements in write characteristics that is particularly required for magnetic heads to achieve higher recording density. On the other hand, if the track width is reduced, write characteristics such as an overwrite property that is a parameter indicating an overwriting capability suffer degradation. Therefore, it is required to achieve better write characteristics as the track width is reduced.
In a magnetic head for perpendicular magnetic recording, it is known that there sometimes occurs a phenomenon in which data stored on a recording medium is erased by a magnetic field produced by the pole layer due to residual magnetization of the pole layer except when writing is performed, which is hereinafter called a pole erase phenomenon.
The likelihood of an occurrence of the pole erase phenomenon depends on the shape of the track width defining portion of the pole layer. Japanese Published Patent Application 2003-296906 discloses a technique for suppressing an occurrence of the pole erase phenomenon by improving the shape of the track width defining portion of a single pole head. For example, this publication discloses that the distance from the medium facing surface to the boundary between the track width defining portion and the wide portion, this distance being hereinafter called a neck height, is divided by the area of the end face of the track width defining portion taken in the medium facing surface, and a value thereby obtained is made greater than zero and smaller than 0.002 (nm−1).
On the other hand, for the shield-type heads, it has been found out that it is impossible to sufficiently suppress an occurrence of the pole erase phenomenon only by controlling the neck height and the area of the end face of the track width defining portion taken in the medium facing surface. This is assumed to relate to the fact that the shield-type heads are different from the single-pole heads in that the shield layer is located near the pole layer in a neighborhood of the medium facing surface.
Japanese Published Patent Application 2004-295987 discloses a technique for ensuring write characteristics by satisfying conditions of NH ≦ W1+0.05 μm and 0.5<NH/TH<1.6, where TH (μm) is the distance from the medium facing surface to the point at which the space between the pole layer and the shield layer starts to be greater than the space between the pole layer and the shield layer taken in the medium facing surface (the distance being hereinafter called a throat height), W1 (μm) is the track width, and NH (μm) is the neck height.
As previously described, if the track width is reduced to achieve higher recording density, it is required to further reduce the neck height NH and the throat height TH for preventing degradation in write characteristics. However, if the throat height TH is made too small, saturation of magnetic flux occurs in a portion of the shield layer from the medium facing surface to the point at which the space between the pole layer and the shield layer starts to be greater than the space between the pole layer and the shield layer taken in the medium facing surface. As a result, the function of the shield layer is degraded, which results in an increase in magnetic flux that is generated from the end face of the pole layer located in the medium facing surface and that extends in directions other than the direction orthogonal to the surface of the recording medium. Therefore, it is not favorable to make the throat height TH too small for achieving higher recording density.